1. Technical Field
Non-limiting, exemplary embodiments relate to a radio frequency identification (RFID) tag for use in an environment of a magnetic resonance imaging (MRI) machine. More particularly, non-limiting, exemplary embodiments relate to a protection device for an RFID tag in an MRI environment so that the RFID tag is not damaged or destroyed by the strong RF fields associated with MRI, and to an apparatus having an MRI machine and an associated RFID tag reading system.
2. Description of Related Art
RFID technology using parasitic RF receive/transmit circuits is widely used to automatically identify articles. RFID technology possesses numerous advantages over traditional identification technology. For example, because RFID technology uses an RF field to operate, no line of sight is required and because it is powered parasitically by received RF signals it requires no internal battery or other power supply. Also, an integrated circuit (IC) chip used in an RFID tag may possess a high memory capacity enabling RFID applications to satisfy more than mere identification purposes. Information stored in the IC chip of the RFID tag may be repeatedly and dynamically changed. The whole RFID tag can be enclosed inside a protective material since the RFID tag does not typically include moving parts. The RFID tag is therefore very robust and reliable. An information transfer process in an RFID tag system does not necessarily require human intervention. Finally, an RFID tag system is reasonably inexpensive. Due to these numerous advantages, RFID technology is used in a wide range of areas such as transportation ticketing, access control, animal identification, electronic immobilization, container identification, inventory control, sporting events and medical applications.
FIG. 1 shows a traditional inductively coupled RFID tag system including a computer 1, an RFID reader 2, an RFID antenna 3 and an RFID tag 5a. The computer 1 is operatively coupled to the RFID reader 2 and includes a memory for storing information. In addition to reading data from the RFID tag 5a (which typically involves two-way RF transmit/receive functions), the RFID “reader” 2 may also be used to perform programming processes. That is, the RFID reader 2 may be used to transmit and write information into a memory of the RFID tag 5a. The RFID tag 5a includes an IC chip 6, an antenna L, and capacitance C. The IC chip 6 provides control functions and a memory for storing data. The data stored in the memory of the IC chip 6 may include information such as inventory, device/product integrity and quality control information. Storing such information in the memory of the IC chip avoids the need for tracking this information with paper.
FIG. 2 shows a traditional capacitively coupled RFID tag system. The RFID tag 5b in this alternative RFID tag system includes a dipole antenna connected to the IC chip 6. While the inductively coupled RFID tag system illustrated in FIG. 1 typically operates at a relatively low frequency (from several hundred kHz to several hundred MHz), the capacitively coupled RFID tag system illustrated in FIG. 2 typically operates at a higher frequency (in the 1.0 GHz range or above).
An information transfer process may begin if the RFID tag 5a or 5b is within operative range of the RFID antenna 3. The RFID industry has developed three typical operating ranges: close-coupled, proximity and vicinity. In an information transfer process (reading or programming process), the RFID reader 2 emits an RF field data carrier at a specified frequency to the RFID tag 5a or 5b via its own antenna 3. The specified frequency is typically a data-modulated carrier frequency. The RFID tag antenna is tuned to the same carrier frequency as the reader antenna 3. The RFID tag 5a or 5b parasitically derives its operating power from the RF field received from the reader 2. The carrier signal generates enough power (only a small amount is necessary) in the RFID tag 5a or 5b to operate its IC chip 6. The carrier frequency signal emitted from the reader 2 via its antenna 3 is also modulated with information. This information can be de-modulated by the RFID tag 5a or 5b. The RFID tag 5a or 5b performs desired operations according to the received information. The desired operations may include reading, writing, transmitting, etc. The operation of “transmitting” from a passive, parasitic RFID tag refers to the RFID tag communicating information back to an RFID reader in response to receiving the RFID reader's field. The RFID tag communicates information back to the RFID reader by modulating the RFID reader's field.
If coupling between an RFID reader and an RFID tag is inductive (such as at 13.56 MHz), any small change of resonant frequency of the RFID tag can be detected by the RFID reader. This is because the distance (e.g., 1 meter or so) compared with the wavelength is very small (i.e., a near field effect). Therefore, if RFID tag tries to send information to the RFID reader, it changes its own (tag) properties so that the RFID reader knows the tag being changed. Then the information is sent back to the RFID reader. In other words, the RFID tag transmits information to the RFID reader by modulating the RFID reader's RF field.
FIG. 3 shows an equivalent circuit of the RFID tag when its IC chip 6 is powered. The power absorbed by the RFID tag antenna effectively acts as a battery providing electrical power to the IC chip. The RF field strength, the orientation of RFID tag antenna in the RF field and the coupling efficiency between the RF field and the RFID tag antenna determines the capacity of the battery.
The emitted RF power of an RFID reader/programmer is typically less than 1 Watt. The peak RF power of an MRI application (e.g., in the imaged volume) frequently exceeds tens of thousands of Watts. A high power RF field, such as that used in an MRI application, may therefore induce a very high voltage and/or current in the RFID tag antenna. This high voltage and/or current may damage or even destroy the IC chip of the RFID tag. A traditional RFID tag thus may not be used in high strength RF field environments such as MRI applications.